205. The entrance of water, in the first instance, 
seems to be the effect of simple imbibition ; but after 
penetrating the external coat/ the fluid appears to be 
conveyed by a vascular structure. M. Senebier found, 
that if seeds, after being immersed in coloured li- 
quors, were cut into thin slices, they exhibited co- 
loured points through the substance of the cotyle- 
donsj which indicated a vascular structure. The co- 
lour became less and less as it approached the germ ; 
and from the plume of a bean, when cut through, a 
transparent fluid escaped from five vessels, arranged 
in a circular order. The two vessels which united 
the cotyledons to the plantule were full of juice, 
which, on being held up to the light, exhibited a 
slight tinge of colour *. 
206. The agency of heat in promoting the deve- 
lopment of the seed is universally admitted ; but the 
operation of light has been much disputed. From a re- 
view of the facts, we were before led to conclude (3*) 
that light, simply, possessed little power either in 
promoting or retarding germination. M. Michelotti, 
however, supports the opinion of M. Senebier, that 
light is injurious to this process t ' but the experi- 
ments of De Saussure seem to prove that this arises 
only from the operation of the heat that exists in the 
solar beam, when seeds are confined in close vessels; 
for when the same temperature was preserved, they 
germinated equally well in transparent and opaque 
vessels J. 
* Physiol. Veg. v. iii. p. 362. et seq. 
t Philosophical Magazine, v. ix. p. 2 !(?. 
J Recherches. p. 23. 
